Question

Why was the annexation of Texas was opposed by many Americans?

Answer 1

It would uneven the balance between slave states and free states and bring war with Mexico.

Explanation:

The balance between slave and free states was a balance that the nation tried to keep to prevent disaster. The North opposed slavery while the South believed it was alright. Annexing Texas would increase the number of slave states, thus enhancing slave power.

Adopting Texas into the Union would also mean war with Mexico. Texas was land Mexico was hoping to get back. Annexing Texas could come across as a declaration of war.